1. Field of the Invention
The invention is directed to the field of wind turbine generators and more specifically to the area of techniques that improve the operating efficiencies of such turbines.
2. Description of the Prior Art
Although wind can be found everywhere on the planet, and is always blowing somewhere, it is erratic. It is erratic as to where it blows, when it blows, at what speed it blows, the length of time it blows and what kind of wind it is . . . steady, gusting, changing direction . . . or all at the same time. This erratic factor is constantly (conveniently) overlooked when manufacturers and government reports on wind energy claim energy efficiencies from wind turbines. Large 3 bladed horizontal axis wind turbines (“HAWT”) require a “clean” flow of air in a narrow window of speed (generally 10-28 mph) to efficiently produce energy from wind. This is due to the basic design of the turbine and their outdated generators.
Manufacturers have greatly increased the size of their turbine blades and the height of their masts to try and reduce the negative effects of these issues. The wind blows stronger at higher heights above the ground and larger blades more efficiently capture the wind's energy. They are close to the limit of negative return because of the greatly increased weight of the blades and the large increase in initial, shipping, installation and maintenance costs.
The maximum efficiency of a three bladed HAWT is about 45%, if wind is constantly blowing at 18 mph. If one considers typical fluctuating wind energy, the average efficiency drops to about 25%. To be truly efficient a turbine has to operate over a much larger wind speed range and in all types of wind.
Large numbers of 3 bladed HAWTs have been successfully installed worldwide to meet the strategic need to reduce dependency on foreign oil and reduce carbon emissions from coal and oil fired electricity generation plants. However, they are all remarkably similar in overall design and component design and layout.
Although commercially successful, largely due to subsidies, 3 bladed HAWTs have several major issues:                High product, shipping, installation and maintenance costs        Narrow operational window (wind speeds of 10-28 mph=5-13 m/s)        Inability to operate effectively in “turbulent” air        Large land usage requirements (about 5 acres per Megawatt)        Installation sites typically far from users        Environmental and health issues (noise, flicker, wildlife, etc.)        Supply chain and delivery issues (weights of approximately 125 tons and 8000 parts)        Regulatory issues (large delays to obtain licenses)        
It is well known that three bladed HAWTs produce electricity in response to wind motion over their blades and are designed to operate within a narrow range of wind velocities (design window). Wind that is too low in velocity (below the window) will not be sufficient to cause the blades to turn. Wind that is too strong (above the window) causes associated sensors to feather the blades or apply brakes to prevent the blades from turning. Otherwise, the blades would turn to turn too fast for safe operation. (Because wind turbine generators are not in operation when the wind velocity is outside the design window, they generally have low operating efficiencies.) Consequently, the placement of wind turbine generators is critical to their output efficiencies and locations are chosen in which the velocity of wind is predominantly within the design window. The most ideal site would be one where the wind velocities are constantly occurring and remain in the upper range of the design window.
Current 3 bladed HAWTs use generators essentially the same as those powered by diesel engines in the 1940's. They generally weigh about 15 tons and require huge inefficient gearboxes to convert the slow turning propeller blade (80 rpm) shaft to 2000 rpm's to generate electricity. This transmission configuration is the main cause of the 3 bladed HAWTs inability to generate electricity in less than a 10 mph wind and to close down above 30 mph.
Prior art vertical axis wind turbine (“VAWT”) designs, such as is shown in FIG. 1, have been found to be successful in eliminating some of the major issues experienced with 3 bladed HAWTs and at a significantly lower cost. Vertical axis wind turbines (also generally known as Savonius turbines) produce large amounts of torque over a wider range of wind speeds as compared to HAWTs. However, the basic efficiency (ability to capture wind energy) of conventional VAWTs is low when compared to horizontal axis turbines.